Radiation filters



Nov. 12, 1968 J. M. MOCHEL RADIATION FILTERS 2 Sheets-Sheet 1 OriginalFiled Oct. 16, 1959 V/5/5LE V542 INFRARED I600 2000 24 v INVENTOR. Rn amnew Mn V: we m m m U- John M ATTORNEY Nov. 12, 1968 J. M. MOCHEL3,410,710

RADIATION FILQTERS Original Filed Oct. 16, 1959 2 Sheets-Sheet 2 so 8 AI I .5 a so w B Y Lu y J \7 2 1 E \z k IO l o VI,S/8 LE' (vi/3R (NERAREQ400 600 600 1000 aaoo c400 AD A flu/Y More lewan/ m 70 400 600 800 I000I200 I400 RA ma non h A v51. am 779' m 711 INVENTOR. John M. Mochel BYMQJZN ATTORNEY United States Patent 3,410,710 RADIATION FILTERS John M.Mochel, Painted Post, N.Y., assignor to Corning Glass Works, Corning,N.Y., a corporation of New York Original application Oct. 16, 1959, Ser.No. 846,896, now Patent No. 3,202,054, dated Aug. 24, 1965. Divided andthis application Dec. 1, 1964, Ser. No. 422,878

7 Claims. (Cl. 117-333) This application is a divisional applicationbased on Ser. No. 846,896, filed Oct. 16, 1959, now US. Patent3,202,054.

This invention relates to radiation or optical filters particularlyadapted to solar radiation control and to a method of producing suchfilters. It is particularly concerned with a filter utilizing aniridized metal oxide film as the filter means.

The recent architectural trend in the direction of glass as a structuralmaterial has intensified the search for improved means of producing andcontrolling color effects in structural glass. Larger architectural andvehicular glass closures have also rendered more critical the wellrecognized need for an effective and economical means of minimizingthermal effects created by solar radiation. Thus, a practical solarradiation filter could greatly reduce the present need for airconditioning and cooling. The problem of meeting such needs iscomplicated by the degree of visible light transmission required in sometypes of closures, e.g. vehicle windows, being greater than that desiredor even tolerable for other purposes.

Special heat absorbing glasses have been proposed as a means ofachieving solar energy control in architectural and vehicular closures.Such glasses are relatively inefficient for the purpose because much ofthe heat which they absorb ultimately is transferred to interior areaseither by conduction and convection currents or by secondary radiationfrom the glass. Also, the effective ingredients in these glasses, minoramounts of colorant oxides, render them generally difficult andexpensive to melt homogeneously and reproducibly. This is particularlytrue in large glass melting units from which sheet glass is ordinarilyproduced.

It has also been proposed to employ various types of thermallyevaporated films. Such films are potentially much more effective sincethey operate on the principal of reflection rather than absorption ofthe heat producing radiation. However, except for small items such asoptical lenses and the like, it is generally impractical and tooexpensive to produce such films. This is particularly true in connectionwith large glass sheets or plate such as are used in producing vehicleor building closures.

It is a primary purpose of this invention to provide an improvedradiation filter adapted to meet the need set forth above. A furtherpurpose is to provide radiation filters adapted to control transmissionin the visible and/ or infrared portions of the spectrum. A furtherpurpose is to provide an improved method of producing large radiationfilters having superior clarity, uniformity and color adaptability.Another purpose is to provide a practical and flexible method ofproducing such filters.

A radiation filter in accordance with this invention comprises arefractory substrate and an iridized metal oxide film having areflectance peak of at least 25% in the near infrared radiationspectrum, the film being composed of at least one oxide of the group ofmetals having atomic numbers from 22-29 inclusive. For maximum infraredrefiectance the film preferably consists of iron or cobalt oxide.

Where maximum transmission of radiation in the visible portion of thespectrum is desired, a clear transparent glass substrate, e.g. aconventional silicate glass,

3,410,710 Patented Nov. 12, 1968 will ordinarily be employed. Wherevisible transmission is not a factor, a colored glass or other knownrefractory substrate material may be employed.

An iridized film is formed by thermal or thermo-chemical decompositionof a metal compound at or on a heated substrate surface to form a thinadherent metal oxide film on such surface. The film may alternatively beformed by pyrolysis of a compound such as an organometal compound or byhydrolysis of a metal compound such as a metal chloride and subsequentpyrolysis or thermal dehydration of such hydrolized salt. Generally, thecompound to be decomposed is applied to the substrate surface in theform of a vapor or atomized solution, although it is also known to applya metal compound on a cold substrate and heat the coated substrate toproduce the desired decomposition.

The invention is more fully described with reference to the accompanyingdrawings in which;

FIG. 1 is a front elevation of a glazing unit illustrating a typicalembodiment of the invention,

FIG. 2 is a sectional view along line 22 of FIG. 1,

FIG. 3 is a sectional view illustrating a modified form of theinvention,

FIG. 4 is a graphical illustration of the relative energy in solarradiation as a function of wave length,

FIG. 5 is a graphical illustration of the reflectivity of iridized ironoxide films as a function of film thickness and wave length, and

FIG. 6 is a corresponding graphical illustration for cobalt oxideiridized films.

In FIG. 1, exterior building wall 10 includes a window, generallydesignated 12, comprising a single sheet of iridized glass mounted in aframe 16 and afiixed in wall 10 in any conventional manner. As shown inFIG. 2, iridized window 12 is composed of a conventional sheet of transparent glass 20 and a thin adherent film of a metal oxide 22 formed onthe outer or exterior surface of the sheet as installed in wall 10. FIG.3 illustrates a modified type of radiation filter which may for exampleinclude a sheet of glass 30 corresponding identically with glass sheet20 of FIG. 2. Glass sheet 30 has a plurality of iridized metal oxidefilms 32-36 formed on its surface in superimposed relationship. Thearrangement and nature of these superimposed films will be discussedsubsequently.

The relative thermal effects resulting from solar radiation areparticularly Well illustrated in the graphical illustration of FIG. 4taken from an article by Moon in the Journal of the Franklin Institute,vol. 230, p. 553 (1940). In this illustration, the relative amounts ofthermal energy resulting from different wave lengths of solar radiationare shown in terms of percentage. The largest thermal effect, at a givenwave length, occurs in the range of visible radiation, that is in thevisible portion of the spectrum from about 400 to 700 millimicrons.However, the overall thermal energy contribution from radiations in theso-called near infrared region, that is from about 700 to 1400millimicrons, approximates that from the visible region. In contrast,radiations beyond 1400 millimicrons, that is in the far infrared,produce a comparatively minor thermal effect. This suggests that maximumbenefits from a thermal standpoint, can be achieved by controllingradiation either in the visible or in the near infrared regions. Formany purposes however, particularly in architectural and vehicularclosures, the amount of radiation dissipation that may be tolerated inthe former region is limited by visual requirements. Thus, it has beenproposed that for architectural closures visual transmission on theorder of at least 30% of normal is desirable. Vehicle closures willnormally have a considerably higher requirement, whereas in decorativestructural glass visible transmission may be immaterial.

The present invention is based in part on my discovery that filters,capable of providing a peak reflectance of at least 25% in the nearinfrared, can be provided by pyrolyzing compounds of the metalstitanium, vanadium, chromium, manganese, iron, cobalt, nickel andcopper, either singly or in combination, to form iridized films of thecorresponding metal oxides on neutral or transparent glass substrates.In particular, cobalt and iron oxide films may have an unusually largereflectivity in the near infrared region which is a complex function oftheir reflectance characteristics and the thickness of the iridizedfilm.

Metal oxide films in accordance with the invention are colored filmshaving a varying degree of absorption for radiations in the visibleportion of the spectrum depending on film composition and thickness. Aspointed out earlier with reference to heat absorbing glasses, absorptionhas been recognized as a much less effective means of thermal control. Ihave found however, that the same considerations apply to a much lesserdegree where, as in the present filters, absorption occurs in a film onthe external surface of a glass substrate rather than in the substrateitself. Accordingly, the present colored films are not only advantageousbecause of their reflectance characteristics but also are much moreeffective as radiation absorbing media as well.

The effect of film thickness is illustrated in FIGS. 5 and 6 whichrespectively show the reflectance characteristics of iron and cobaltoxide films in three different optical thicknesses. Each graphicalillustration depicts reflectance in terms of percent at differentradiation wave lengths. In FIG. 5 curves A, B and C show the reflectanceof iridized iron oxide films which are respectively 1500, 2300 and 5,000Angstrom units thick in terms of optical thickness. correspondingly,curves D, E and F of FIG. 6 show the reflectance characteristics ofiridized cobalt oxide films having optical thicknesses of 1,000, 2,000and 3,500 Angstrom units. As is well known, optical thickness representsabsolute thickness divided by the film refractive index. Hence absolutethickness is on the order of two to three times the indicated opticalthickness. It will be observed that with each type of film, an optimumreflectance in the near infrared region and an optimum or relativelyhigh transmission in the visible region is obtained with a film havingan optical thickness of about 2,000-2,500 Angstrom units. Thereflectance peak, i.e. the point of highest reflectivity, for this filmthickness occurs at a wavelength of about 900 millimicrons andapproaches 50%.

Where a relatively low degree of visible transmission is eitherdesirable or may be tolerated, a considerably higher reflectivity in thenear infrared as well as the visible region can be obtained with amultiple film arrangement such as shown in FIG. 3. In such anarrangement alternate film layers 32 and 36 are composed of a relativelyhigh index, reflecting oxide, e.g. either cobalt or iron oxide, forreflectance purposes. These reflecting films are separated by a clearcolorless iridized metal oxide film 34 having a low refractive index.For this purpose iridized amorphous silica or alumina films ofapproximately the same optical thickness as the cobalt or iron oxidereflecting films, and having a refractive index approximating till: 1.5value of ordinary lime glass, are particularly suita e.

A multilayer film of this nature is particularly effective since itprovides a maximum amount of infrared radiation reflectance with aminimum absorption effect on visible radiations. Thus the absorption inthree spaced reflecting films of about 2000 A. units thickness each willbe approximately that of a single 6000 A. reflecting film. However,reflectance remains essentially unchanged regardless of single filmthickness since reflectance, unlike absorption, is a function of filminterfaces. While secondary refieetions cause some interference, thetotal reflection from a multilayer film is approximately a function ofthe numher of interfaces or spaced reflecting films. Thus, we may assumereflection and transmission of near infrared at the initial interface inFIG. 3, i.e. the 34-36 interface. Then, of the 60% transmittedradiations, another 40% reflection occurs at the glass-film interface3032 this being 24% of the original infrared radiations reaching thefilter. Total reflection then will be 64%. It will be apparent that athird reflection, as would occur in a five layer film, would be about13% and would provide an overall reflection of about 77% of the originalinfrared radiation.

The extent to which the reflecting films and spacer films may bemultiplied is relatively unlimited. However, optical quality usuallydiminishes and visible transmission decreases as a function ofincreasing thickness. Consequently, a five layer film, that is threereflecting films and two spacing films, is usually the maximum feasible,the overall illumination level with such a multilayer cobalt or ironoxide filter being about 25% of normal unfilmed glass.

If the thickness of all the layers in a multilayer film are preciselythe same, the reflection peak will be narrow and high; if there is somevariation in thickness, the reflection peak will be broader and notquite as high. The latter situation usually occurs even when closecontrol is exercised over the relatively non'precise pyrolysis method offorming films. This broadening is desirable since a generally highreflection band extending from approximately 650 millimicrons to about1300 or 1400 millimicrons may be produced in this manner. Howeverthickness variations greater than :10%, are generally detrimental andshould be avoided.

Various iridizing-"processes are known and various metal compounds maybe successfully employed. However, for present purposes I have foundthat the use of metal derivatives of the 1,3-beta diketonates,preferably the acetyl acetonates, either in vaporized or atomizedsolution form, provide a distinctly superior iridizing atmosphere. Inproducing optical filters of any nature, uniformity is highly desirable.In iridizing, particularly where large surfaces are involved, it isdifficult to achieve this uniformity of film thickness. One cause isuneven cooling of the substrate and avoidance of a water solutionminimizes this effect. Even as compared to other organic solutionshowever, the diketonates generally provide a much more uniform iridizedfilm. The reason for this is not entirely understood but is believed tobe associated with compound stability whereby the atmosphere spreadsuniformly over the surface before decomposition by pyrolysis occurs.

It is also found that haziness, particularly on soda lime type glass isminimized by using this type of metal compound. The acetyl acetonates ofall of the metals are readily volatilized or atomized in organicsolution, thus facilitating iridizing. Furthermore, the acetylacetonates of these metals are mutually compatible, thus permittingmixtures to be applied for modified color effects.

It will be understood that the metal diketonate may be prepared and usedas such or another compatible metal salt may be mixed with the diketonecompound, the latter also effectively stabilizing the iridizing solutionas explained earlier. Acetyl acetone is a commercial synonym for thechemical term 2,4-pentane dione.

I have further found that iridized films of the metal oxides enumeratedabove provide a variety of reflected light colors for architecturalglass decorative purposes. Also, as shown below, the oxides may beemployed in combination to provide an even greater range of coloreffects. This obviates prior difliculties in reproducibly meltingcolored glasses and providing desired color variations. With thisinvention conventional sheet glass can be drawn or rolled continuouslyand a range of color filter and uncolored glass products may be producedmerely by employing selected iridizing materials as required. Thispermits melting of a single, uncolored glass for all purposes.

By way of further illustrating the invention and its practice, thefollowing specific examples are presented:

EXAMPLE 1 An iridizing solution was compounded by dissolving ferricacetyl acetonate in methanol in the ratio of:

Ferric acetyl acetonate grams 1O Methanol cc 100 A plate of clearborosilicate glass was heated to a temperature of 625 C. in a furnaceand quickly moved under a conventional spray gun for application of thesolution as an atomized spray. Exposure was of such duration as toprovide an iron oxide film having an optical thickness of about 2000 A.on a plate surface of about square inches. The filmed plate hadreflectance characteristics as shown by Curve B in FIG. 5, and a goldenbrown visual appearance by reflected light.

The thickness may be visually gauged by comparison with a referencestandard measured spectrophotometrically. Such standard will have athickness between 1st order red and 2nd order blue as measured by thewell known principle of interference colors. Since this is not sharplydistinctive, one may also base thickness on the basis of applying 6.5cc. of solution to an area of about 10 sq. in. in a period of aboutseven seconds at the indicated temperature.

EXAMPLE 2 A glass plate filmed with an iron oxide in accordance withExample 1, was reheated to 625 C. and exposed at such temperature to anatomized atmosphere of an aluminum compound solution composed of thefollowing materials in the indicated proportions, the aluminum being atleast partially in the form of aluminum acetyl acetonate:

A1(NO -9H O grams 10 Acetyl acetone cc 1O Methanol cc.. 5

The exposure time was such as to produce a film correspondingapproximately in thickness to that of the iron film. The same amount ofsolution 6.5 cc., was employed to produce the desired thickness. Theresulting film is composed of an amorphous form of alumina, is visuallycolorless and has a refractive index of approximately 1.5.

Thereafter the filmed glass plate was reheated to 625 C. and a secondiron oxide film corresponding to that described in Example 1 produced byrepeating the procedure described there.

EXAMPLE 3- Alternatively, an iridized alumina film, as described inExample 2, maybe produced from the following solution:

Aluminum acetyl acetonate grams 10 Benzene cc 100 A ten square inch filmhaving an optical thickness of about 2000 A. is produced by applicationof about 5 cc. of solution. However, the substrate must be heated toabout 675 C. and the solution of Example 2 is preferred because of thelower temperature. It is thought the nitrate may accelerate oxidationand A1 0 formation from the diketonate complex at the lower temperature.

In producing aluminum acetyl acetonate, a solution of 20 grams aluminumnitrate in 50 cc. B 0 is stirred rapidly into a solution of 6 cc. 28%ammonium hydroxide, 16 cc. acetyl acetone and 75 cc. H O. Theprecipitate of aluminum acetyl acetonate is thoroughly washed and driedfor use.

A multilayer film, formed in the described manner and embodying threeiron oxide films and two alumina films, was found to provide areflectance peak of about 80% as compared to a peak of about 40% for theinitial single layer of iron oxide.

EXAMPLE 4 The procedure described in Example 1 was repeated except thatthe following iridizing solution was employed:

Cobalt acetyl acetonate grams 10 Methanol cc Pyridine cc 10 Theresulting filmed glass, having a thickness of about 2000 A., had a lightgreenish brown appearance by reflected light, and had a reflectancecurve corresponding to that shown as Curve E, FIG. 5.

A multilayer film filter was produced in a manner corresponding to thatdescribed in Example 2 and had similar reflectance characteristics inthe near infrared.

EXAMPLE 5 A chromium oxide film having an optical thickness of about1700 A. was formed by spraying about 5 cc. of the following solution ona 10 sq. in. section of sheet glass heated to a temperature of 625 C.:

EXAMPLES 7-10 The following solutions were employed in like manner toproduce the corresponding metal oxide films:

Vanadium acetyl acetonate grams 2 Methanol 10 Pyridine cc 1 Copperacetyl acetonate grams 10 Methanol 100 Diethylene triamine cc l0Manganese acetyl acetonate grams 20 Methanol 00-- 50 Pyridine cc 5Titanium tetra isopropoxide cc 30 Benzene cc 100 Acetyl acetone c 40Colors produced with the various oxides are:

CuO Reddish brown. NiO Light green. C00 Dark brown. Fe O Amber to deepred. MnO Brown.

Cr O Green. V 0 Dark brown. TiO Colorless to blue.

The depth of color is dependent on film thickness in large degree.

EXAMPLE 11 A mixture in about equal parts of the chromium solution ofExample 5 and the cobalt solution of Example 4 was sprayed on a glasssurface at 625 C. The resulting film was a neutral gray color whichprovided substantially uniform light transmission across the visibleportion of the spectrum.

EXAMPLE 12 A neutral gray film similar to that of Example 11 wasproduced from a mixture of the chromium solution with 7 the nickelsolution of Example 6 in equal parts. Substantial predominance of eithersolution in the mixture of Examples 11 or 12 produce films tendingtoward the color characteristics of the corresponding predominant metaloxide.

EXAMPLE 13 The copper and manganese solutions of Examples 8 and 9 weremixed in ratios varying from 20 to 80% of each solution. The filmsresulting from spraying the mixed solutions produced a neutral densitytype film having a bluish tint. Thus, a film of about 2000 A. opticalthickness provided a substantially straight transmission line across thevisible region varying from 50% transmission at the blue end to about40% transmission at the red end.

EXAMPLE 14 A neutral gray film was also produced from a mixture of thecobalt and manganese solutions of Examples 4 and 9.

What is claimed is:

1. A method of producing a radiation filter which comprises heating arefractory substrate to a temperature of 500800 C., exposing the heatedsubstrate to an atmosphere containing a 1,3-beta diketonate of at leastone metal having an atomic number from 22 to 29 whereby said metaldiketonate is pyrolyzed to form an adherent clear metal oxide film ofuniform thickness on the substrat surface.

2. A method in accordance with claim 1 in which the diketonate is anacetyl acetonate.

3. A method in accordance with claim 2 in which, after the filming stepthere recited, the filmed substrate is exposed to an atmospherecontaining an acetyl acetonate of aluminum and thereafter exposed to anatmosphere as defined in claim 2, the substrate being maintained at atemperature of 500-800 C. and a film of the corresponding metal oxidethereby being deposited during each such exposure.

4. A method of producing an aluminum oxid film on a refractory substratewhich comprises maintaining the substrate at a temperature within therange of 500-800 C. and exposing the hot substrate to an atmospherecontaining a 1,3-beta diketonate derivative of aluminum.

5. An improved method of producing colored, heat reflecting, structuralglass which comprises forming a continuous flat sheet of glass,maintaining such sheet at a temperature within a range of 500800 C.While exposing a surface thereof to an iridizing atmosphere containing a1,3-beta diketonate of at least one metal having an atomic number from22-29 to form on such surface an adherent film of the correspondingmetal oxide.

6. A method in accordance with claim 5 wherein the surface of the glasssheet is exposed to the iridizing atmosphere for a time sut'licient toproduce a metal oxide film having an optical thickness of about2000-2500 A.

'7. The method of forming adherent metal oxide films on non-porousrefractory substrates which comprises the steps of: preparing a solutionconsisting of an organic solvent and at least a plurality of differentmetal acetylacetones wherein the metals are selected from a groupconsisting of chromium, manganese, iron, cobalt, nickel, and copper;heating the substrate to a temperature greater than about 500 C. butless than the melting and sublimation temperatures of the substrate andoxides of the metals, whichever occurs first; atomizing the solution;and directing the atomized solution against the heated substrate in airso long as the substrate surface remains hotter than a temperaturegreater than about 500 C. to yield a structure on the substrate surfacewhich contains only oxides of th metal acetylacetones, and repeating thelast mentioned step as many times as necessary to attain a filmcorresponding to a predetermined thickness.

References Cited UNITED STATES PATENTS 2,430,520 11/1947 Marboe117--107.2 2,628,927 2/1953 Colbert et al. 1l7-33.3 2,734,874 1/1956Drake 117106 2,564,708 8/1951 Mochel 117-333 2,692,836 10/1954 McAuley117-54 2,698,812 1/1955 Schladitz 117107.2 2,833,676 5/1958 Heibel etal. 117-107.2 2,831,780 4/1958 Deyrup 117--106 3,081,200 3/1963 Tompkins1l7--106 ALFRED L. LEAVITT, Primary Examiner.

A. G. GOLIAN, Assistant Examiner.

1. A METHOD OF PRODUCING A RADIATION FILTER WHICH COMPRISES HEATING AREFRACTORY SUBSTRATE TO A TEMPERATURE OF 500*-800*C., EXPOSING THEHEATED SUBSTRATE TO AN ATMOSPHERE CONTAINING A 1,3-BETA DIKETONATE OF ATLEAST ONE METAL HAVING AN ATOMIC NUMBER FROM 22 TO 29 WHEREBY SAID METALDIKETONATE IS PYROLYZED TO FORM AN ADHERENT CLEAR METAL OXIDE FILM OFUNIFORM THICKNESS ON THE SUBSTRATE SURFACE.